1. Field of the Invention
This invention relates generally to a frozen dessert dispenser in which a pack containing a frozen dessert such as ice cream or frozen yogurt and accommodated in a dispensing cylinder is pressurized by a pistons thereby dispensing the frozen dessert, and more particularly to an improvement in a driving mechanism for driving the piston in such a frozen dessert dispenser.
2. Description of the Prior Art
International Publication No. WO 90/05697 discloses one of the frozen dessert dispensers of the above-described type. In the disclosed dispenser, a cylinder is provided in a heat-insulating box in a vertical disposition. An atmosphere in the heat-insulating box is cooled by a cooling unit. A packed frozen dessert such as a packed ice cream is accommodated in the cylinder. The pack is compressed by a piston driven by a fluid pressure so that the ice cream in the pack is dispensed through a communicating pipe out of the heat-insulating box. In this construction, a refrigerant such as brine is used as an operating fluid as well as air. A pump is driven to supply the refrigerant into a pressure chamber of the cylinder and to suck the refrigerant out of the pressure chamber.
When all of the frozen dessert is dispensed out of the pack, the pump is driven in a reverse direction to suck the operating fluid so that a piston is descended. As a result, the capacity of a pack accommodating chamber in the cylinder is increased so that the pack is replaced by a new one. In replacement of the pack, the operator conventionally confirms the piston assuming a bottom dead point by visual inspection and then stops the pump. However, since there is a time lag between the reach of the piston to the bottom dead point and the stop of the pump, the sucking operation is continued a moment after the piston has descended to the bottom dead point. This reduces the pressure in the pressure chamber of the cylinder to a large extent. As a result, the pump is overloaded such that the service life thereof is shortened or an offensive noise is produced.
When the frozen dessert dispenser in which a liquid such as brine is used as the operating fluid is operated for the first time after installation, the pump is driven so that the operating liquid is supplied from a brine tank disposed in a freezing compartment into the cylinder. In this case, air is sometimes confined or cooped in a pipe at the discharge side of the pump or in the interior of the cylinder below the underside of the piston. Further, in a case where a sealing member used in the piston is deteriorated during an ordinary operation, air sometimes leaks from the interior of the cylinder over the top of the piston to the interior of the cylinder below the underside of the piston when the operating fluid is sucked so that the piston is descended. As a result, the leaked air is sometimes mixed into the operating fluid in the interior of the cylinder below the underside of the piston. When the operating fluid is pressurized in the pressure chamber in the above-described condition, the air below the piston is also pressurized. Since air is a compressive fluid, the air is first compressed to the limit thereof and thereafter, the piston is pressurized by the operating fluid to be ascended. This renders the movement of the piston unstable. This problem cannot easily be coped with when a driving time of the pump is controlled for the dispensing of a constant amount of frozen dessert, for example.
Therefore, an object of the present invention is to provide a frozen dessert dispenser in which the pump can be prevented from being driven notwithstanding reach of the piston to a limit position when the piston is descended, whereupon the pressure chamber of the cylinder can be prevented from being excessively decompressed.
Another object of the invention is to provide a frozen dessert dispenser in which an adverse effect by the air mixed with the operating liquid can be eliminated so that the piston can stably be driven.
Further another object of the invention is to provide a frozen dessert dispenser which can prevent the frozen dessert and/or the operating fluid from scattering outside the dispenser when a lid of the cylinder is incompletely closed or the operating fluid leaks out of a supply passage thereof in a case where the dispenser is inadvertently manipulated for the dispensing operation with a door of the heat-insulating box being open.
The present invention provides a frozen desert dispenser comprising a heat-insulating box having a side formed with an opening closed and opened by a heat-insulating door, a cooling unit for cooling an atmosphere in the heat-insulating box, a dispensing cylinder formed into the shape of a vessel and having an open end, the cylinder including a lid for closing and opening the open end thereof and a piston provided therein for sliding motion, the cylinder including a pack accommodating chamber defined between the piston and the lid therein so that a frozen dessert pack is accommodated into the pack accommodating chamber when the lid is opened, a pump supplying and discharging an operating fluid to and from a pressure chamber defined in the dispensing cylinder, the pressure chamber being located in a space opposite the pack accommodating chamber with respect to the piston, and a usually closed operating fluid introducing port provided in the cylinder, the operating fluid introducing port being opened so that the operating fluid is introduced therethrough into the pressure chamber, when the piston reaches a bottom dead point.
According to the above-described construction, when the piston reaches the bottom dead point thereof, the operating fluid introducing port is opened so that the operating fluid is introduced into the pressure chamber in the dispensing cylinder. Consequently, the interior of the pressure chamber can be prevented from being subjected to an excessive negative pressure.
In one preferred form, the frozen dessert dispenser further comprises an auxiliary passage connecting the pressure chamber of the dispensing cylinder and a brine tank to each other, a check valve provided in the auxiliary passage so as to allow the operating liquid to flow from the brine tank to pressure chamber and so as to prevent a reverse flow of the operating fluid, and a valve provided in the auxiliary passage to be in series to the check valve, the valve being opened when the piston reaches a bottom dead point, the valve being closed otherwise.
In this construction, when the piston reaches the bottom dead point thereof, the valve is opened so that the operating liquid in the brine tank is caused to flow via the check valve into the pressure chamber. Consequently, the interior of the pressure chamber can reliably be prevented from being subjected to the excessive negative pressure. Thereafter, when the pump is driven to increase the pressure in the pressure chamber, the check valve shuts off the flow of the operating liquid from the pressure chamber toward the brine tank, whereby the piston can immediately be ascended.
In another preferred form, the frozen dessert dispenser further comprises an air removing element which removes air from the pressure chamber. Air is removed from the operating liquid supplied into the pressure chamber. Consequently, the piston can smoothly be moved when the operating liquid is pressurized. The air removing element may include an air removing pipe connecting the brine tank and a backside of the piston when the piston reaches a bottom dead point thereof, and a valve or a throttle valve each provided in the air removing pipe. Further, the air removing element may include an air removing pipe extending through opposed sides of the piston, and the air removing pipe may usually be closed by a cock detachably attached thereto.
A brine tank for reserving the operating fluid is preferably provided in the heat-insulating box to be away from a bottom of the heat-insulating box so that a passage for a cooling air is defined between the brine tank and the bottom of the heat-insulating box. Moreover, the brine tank is preferably further provided to be away from a rear fade of the heat-insulating box so that a passage for the cooling air is defined therebetween. Consequently, the operating liquid is sufficiently cooled such that the frozen dessert can be prevented from being heated when the operating liquid is supplied into the dispensing cylinder.